The present invention relates to mechanisms for driving analog signals across transmission medium. In particular, the present invention relates to a low voltage supply line driver capable of providing relatively high voltage output with a low power supply voltage.
Advances in semi-conductors have led to increased speed, lower power consumption, and higher levels of integration in digital circuits. In general, analog circuits have not benefited equally from process advancements due to the inability to utilize minimum size transistors and the reduction in power supply voltages. Successful mixed-signal design in state of the art semi-conductor processes requires efficient, low-voltage analog topologies.
Ethernet systems typically use line drivers as part of a process for converting digital data into an analog signal for a transmission line. One basic line driver topology is referred to as a 10Base-T Ethernet driver. The specification for the 10Base-T Ethernet line driver is defined by the IEEE 802.3 industry standard. One aspect of this specification is that the Ethernet line driver must provide sufficient current to enable an output voltage to be generated at a level of 2.5+/xe2x88x920.3Vpk.
Typically, Ethernet line drivers use external voltage supplies that are large enough to enable the line drivers to provide the required output voltage levels. But with advancements in semiconductor processing, devices used in line drivers are increasingly becoming smaller. The smaller devices come with smaller voltage tolerances. These devices have limited use in Ethernet line drivers if their voltage tolerances is less than the supply voltage required for generating the required output voltage.
In addition, attempts to use smaller devices in Ethernet line drivers have had difficulty generating necessary output voltage swings required by the industry standard. The voltage swings within the line drivers cannot cause voltage drops to appear across devices that have a smaller voltage tolerance. The small tolerances may cause those devices to breakdown as a result of the voltage swings.
Embodiments of the invention include a line driver for driving an output signal onto an output having a first terminal and a second terminal. A first current driver is coupled to the first terminal of the output. A power supply having a voltage X is supplied to the first current driver. The first current driver is capable of providing a first current to the first terminal. The first current is sufficient to cause an output voltage having a magnitude Y to appear across the output, where the magnitude Y is greater than the voltage X. The first current driver includes a first plurality of elements to provide the first current. Each of the plurality of elements has a maximum voltage tolerance that is less than the magnitude Y.